Polymer composites form a new class of very useful materials that are used increasingly in various devices for a wide range of applications in the field of photonics (photoconductivity, photolimitation, linear and non-linear optical materials), electronics (capacitors), and various sensing devices. As reported in the literature, polymers that are doped often exhibit a substantial improvement in performance over that of the matrix.
Techniques for large scale fabricating polymer composites include flash evaporation, extrusion, and monomer spreading and curing. The curing of the monomer formulation is done either by thermal means or by radiation. In radiation curing, it is desirable for the monomers or monomer mixtures to have an average of at least two double bonds. This reactivity assures a high speed cross-linking when exposed to the radiation source. For flash evaporation, formulations containing electron acceptor dopants and electron donor substances are evaporated at temperatures above their boiling point and well below the decomposition point and thus are not degraded by the deposition process.
Vacuum flash evaporation of a monomer formulation, as described in U.S. Pat. Nos. 4,954,371, and 5,681,615, is done by introducing a misted liquid formulation into an evaporator which is heated at a temperature above the boiling points of the components and below the temperature which causes the degradation and/or polymerization of the monomers. Upon contact with the evaporator wall, the liquid droplets are flash-evaporated. The vapor, upon contact with a cooled substrate surface, condenses into a thin liquid layer that is subsequently radiation-cured, to form a thin homogeneous polymer composite film.
The existing commonly used methods for fabricating organic polymer photonic films are solvent based relatively slow coating techniques; see, e.g., Y. Wang, "Photoconductivity of Fullerene-Doped Polymers", Nature, 356-585 (1992); R. Burzynski et al, "Novel Optical Composites: Second-order Nonlinear Optical and Polymeric Photorefractive Materials for optical Information Storage and Processing Applications", Optical Engineering, 35(2), 443 (1996); and D. S. K. Mudigonda et al, "Polymer Blends and Copolymers Based on N-Vinylcarbazole and N-Phenyl-2(2'thienyl)-5-(5"-vinyl-2"-thienyl)pyrrole: A Novel Approach to Tailor Electrochromic Properties", ACS Polymer Preprints, 39(1), 139(1998).
On the other hand, vacuum flash evaporation followed by radiation curing technique provides high quality, pinhole-free polymer films with controllable thickness and uniformity. Therefore, it is of great interest to have a method for processing both the homogeneous solutions and the heterogeneous mixtures containing electron acceptor dopants and electron donor materials with radiation curable monomers in order to fabricate optical polymer composite films.